1. Field of Invention
The invention relates generally to stringed musical instruments and more particularly to musical instruments using feedback to provide sound sustaining special effects.
2. Background Art
U.S. Pat. No. 3,742,113 issued to Marcus S. Cohen on Jun. 26, 1973 discloses a stringed musical instrument with electrical feedback including a means responsive to the vibrations of a string as it is plucked or hit and a means for driving the oscillations of the string electronically. Pickups in the form of coils wound around magnetized cores produce electrical signals responding to the vibrations of the strings. The signals are then amplified and converted to sounds via loudspeakers. The pickups are affixed to the instrument adjacent the strings. Means are disclosed wherein the string's vibrations can be sustained for an arbitrary period of time at its fundamental frequency or at higher harmonics thereof, or at a mixture of fundamental and harmonics, producing a sound rich in overtones unique to the instrument. The player selects which of the plurality of strings will be driven continuously, which will be driven only when played upon, and which will remain undriven.
As described by Cohen '113, the effect of the invention is to make possible the creation of aesthetically pleasing sounds which are entirely different than those created by standard stringed instruments. As pointed out, contemporary musicians have sought and continue to seek methods of achieving effects which are different from those to which audiences are accustomed. Such effects are generally welcomed and have resulted in the creation of new musical forms and techniques.
U.S. Pat. No. 4,075,921 issued to Gregory S. Heet on Feb. 28, 1978 discloses a string instrument vibration initiator and sustainer device which senses the vibration of a string and provides an output driving signal for sustaining the vibration. In one embodiment described, a hand held device is positioned above a vibrating string in an instrument for sensing the vibration of the string. The sensed vibration is electronically amplified and then coupled to a coil which is used to drive the same string. In another embodiment, pickup coils and driving coils are permanently located adjacent to the strings of the instrument.
U.S. Pat. No. 4,245,540 issued to Barry A. Groupp on Jan. 20, 1981 discloses a sound sustaining device for musical instruments such as a guitar which controllably and selectively sustains musical sounds produced by the instrument. The device includes an electrical pickup proximate to the strings of the guitar for generating electrical signals which correspond to the vibrations of the strings. The signals are amplified by the device and are converted to a loudspeaker mounted to the guitar and proximate the strings wherein mechanical vibrations sympathetically reinforce the initial vibrations and maintain the strings in a vibratory state and thereby sustain the sound.
Consideration of some of the many terms and effects used in the musical art will provide appreciation for the art of musical enhancement and special effects and support the teaching of the present invention. By way of example, consider a few such effects and terms. A signal processor comprises an electronic circuit which alters an audio signal in some unique fashion. By way of example, therefore, an equalizer, filter, compressor, phaser, delay line and other similar sound altering devices are considered signal processors. Many signal processors are used for special effects such as flangers and distortion generators (fuzz boxes) used by electric guitarists as discussed in the "Sound Reinforcement Handbook" written for Yamaha by Gary Davis and Ralph Jones. As further described in the Handbook, other signal processors are used to subtly shape the overall sound balance (equalizers), or used to control the perceived spaciousness (reverberation and delay), or to level the wide volume variations in a program (compressors) in such a way that no special effect is perceived. These same devices are used for mild enhancement and extreme special effects. It is these special effects and sound enhancement results with which the present invention deals.
To further appreciate the need for the present invention, consider the following definitions and the methods currently used in the art to create various sound enhancements. As defined in the Handbook, Reverberation consists of multiple, blended sound images (not individually discernible echoes) caused by reflection from walls, floor, ceiling and other surfaces which do not absorb all the sound. Reverberation occurs naturally in most indoor environments, and is more prominent with hard surfaced environments. Reverberation is also created artificially by echo chambers and from electronic reverberators and are used for live sound reinforcement, broadcast and recording.
Flanging was originally achieved using reel-to-reel tape recorders. Two tape recorders would record and play back the same programs, in synchronization. By alternately slowing down the machines, different phase cancellations occur. The slowing down was achieved by applying hand pressure against the flanges of the tape supply reels, hence the term flanging. The alternately slowing down one machine and then the other, with both outputs electronically mixed, causes a series of changing interactions between the two outputs. Reinforcement (addition) and cancellation (subtraction) occurred giving the effect of a sweeping comb filter. The sound can be described as swishing.
Flanging and phasing have a somewhat similar sound but are achieved in different ways in the art. A phase shifting device contains a filter having a very narrow frequency bandwidth. A signal is split, with some of it going into the filter circuitry and some bypassing the filter. Increased phase shift is created at frequencies on either side of the filter notch. By sweeping the notch up and down the frequency spectrum, and mixing the resulting signal back with the direct signal, a series of ever changing phase cancellations occurs. Phasing, as well as the aforementioned effects, are especially popular for guitars, keyboards and vocals.